1. Field of the Invention
The present invention relates to an apparatus for rotatively driving a turn table. More specifically, the present invention relates to an apparatus for rotatively driving a turn table, such as a turn table of a record player, and the like.
2. Description of the Prior Art
Various types of appratuses for rotatively driving a turn table, typically a turn table of a record player, have been already proposed and put into practical use. In particular, apparatuses of an idler type, a belt drive type, a direct drive type and the like have been proposed, in order to drive a turn table of a record player. Among other things, it has been observed that an apparatus of a direct drive type for directly driving a turn table by means of a motor shaft without recourse to an idler nor belt is advantageous. A direct current brushless motor has been commonly utilized as a driving motor for an apparatus of a direct drive type. Nevertheless, a conventional direct current brushless motor is expensive and in addition requires a complicated control circuit including a speed detecting scheme for a stabilized revolution. For this reason, a direct current brushless motor has been employed only in high quality record players.
A direct drive type motor which is relatively inexpensive has also been developed, which comprises a rotor including an arrangement of a plurality of permanent magnet pieces of north and south poles disposed alternately and equally spaced along the periphery of a turn table and a stator provided to be opposed only to a portion of the arrangement of these permanent magnet pieces. Because of an arrangement of a stator opposing only to a portion of the permanent magnet arrangement along the periphery of a turn table, such a motor may be referred to as a partial drive type motor. The principle and the structure of such a so called partial drive type motor is disclosed in U.S. Pat. No. 3,922,590 issued Nov. 25, 1972 to Anthony Charles Warren et al. A so called partial drive type motor employing the principle disclosed in the above referenced United States patent may be used in an apparatus of a direct drive type. However, relative movement of the magnetic poles of the rotor and the magnetic poles of the stator alternately gives rise to the maximum attracting force and minimum attracting force depending on the relative displaced amount between these rotor magnetic poles and stator magnetic poles, resulting in uneven revolution of the rotor. For this reason, a conventional partial drive type motor is not preferred for driving a high quality record player. Thus, it is preferred that a so called partial drive type motor of an inexpensive cost be provided wherein the above described problem of uneven revolution is eliminated.